Hydro-pneumatic system with pressure limiting valve

ABSTRACT

A hydro-pneumatic system has an air powered motor driving a hydraulic pump with a pressure limiting valve that turns off air flow to the air motor when a hydraulic pressure output by the pump at a sense port of the valve reaches a certain limit. A valve element of the valve has spring, hydraulic and pneumatic sections, with an unbalanced area of the hydraulic section in a sealed pressure chamber of a cartridge that is part of the valve housing. The pneumatic section extends out one end of the cartridge to fill a bore between the air inlet and outlet ports when the pneumatic section is extended, and allow air to pass when it is retracted.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage entry under 35 U.S.C. §371 ofInternational Patent Application No. PCT/US2007/082504 filed Oct. 25,2007, which claims the benefit of U.S. Provisional Patent ApplicationNo. 60/863,078 filed Oct. 26, 2006.

STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

This invention relates to hydro-pneumatic systems, and in particular tosuch a system having a hydraulically actuated pneumatic valve.

BACKGROUND OF THE INVENTION

Hydraulic systems exist having pumps that are driven by compressed airdriven motors. The peak hydraulic pressures generated by the pump aregenerally significantly greater than the pneumatic pressure used todrive the pump, but in many applications the peak hydraulic pressureobtainable is limited by the pneumatic pressure used to drive the pumpand the operation of the pump relies on the pump stalling when thatpressure is reached. In some of these pumps, the pneumatic motor willnever stall due to leakage, losses, system design or pressure variationin the system. Particularly for these kinds of applications, some othermeans is desirable to cause the pneumatic motor to stop at a given limitof hydraulic pressure.

SUMMARY OF THE INVENTION

The present invention provides a hydraulic system with a pressurelimiting valve that is hydraulically actuated to turn off the flow ofair to the pump drive motor at a certain hydraulic pressure limit. Thevalve has a valve housing having an air inlet port and an air outletport and a hydraulic fluid sense port. A valve element in the housinghas a hydraulic section and a pneumatic section, the hydraulic sectionbeing in fluid communication with the hydraulic sense port and thepneumatic section being in fluid communication with the air inlet portand the air outlet port. The valve element is operable to open fluidcommunication between the air inlet port and the air outlet port in anopen position of the pneumatic section and to close fluid communicationbetween the two air ports in a closed position. The hydraulic sectionhas an unbalanced area in fluid communication with the hydraulic fluidsense port that moves the valve element when a pressure in the hydraulicfluid sense port reaches a certain limit.

In preferred aspects, a spring urges the pneumatic section to the openposition, and the spring force is preferably adjustable. In anotheraspect, the hydraulic section and the pneumatic section of the valveelement are integral with one another, and a cartridge portion of thehousing defines a hydraulic chamber in which the unbalanced area of thehydraulic section resides. The valve element can extend out of thecartridge at one end to a position in which it can close communicationbetween the two air ports, and at the other end of the cartridge, canextend out of the cartridge to be acted on by a biasing spring.

These and other objects and advantages of the invention will be apparentfrom the detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a valve of the invention andschematically illustrating a hydro-pneumatic system incorporating thevalve;

FIG. 2 is a view of the valve like in FIG. 1 but showing the valve in aclosed state; and

FIG. 3 is an end view of the valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a valve 10 of the invention has a housing 12 thatincludes a valve block 14 and a cartridge 16 that is screwed into theblock 14. Valve block 14 has an air inlet port 18 and an air outlet port20. Block 14 also has a hydraulic fluid sense port 22 that is incommunication with chamber 24 of cartridge 16. A valve element 26extends through chamber 24 and has a hydraulic section 28 having anunbalanced area 30 that is inside the chamber 24 and a pneumatic section32 that is extendable into a bore 34 that extends between the two airports 18 and 20. Section 32 fits closely with bore 34 in a sliding fitso that when section 32 is extended into bore 34 section 32 closes offfluid communication between the ports 18 and 20, as shown in FIG. 2.

Valve element 26 extends leftwardly from the cartridge 16 to a springportion 38 surrounded by a compression spring 40 that is compressedbetween axially facing surface 42 of body 14 and a spring reactionmember 44 that is threaded on the end of spring section 38 of the valveelement 26. Turning the element 44 relative to the valve element 26either compresses the spring more in one direction or relieves thecompression on the spring 40 in the other direction to adjust the amountof spring biasing force on the element 26, which force biases theelement 26 to move the pneumatic section 32 into the open position.

Hydraulic fluid introduced to the hydraulic fluid sense port 22 acts onthe unbalanced area 30 in the chamber 24. Unbalanced area 30 is createdby a difference in diameter in the element 26 that occurs betweensliding seals 54 and 56, that creates a shoulder at the junction betweenthe two diameters, identified at 30 in FIG. 1. A sufficient hydraulicpressure in chamber 24 acting on area 30 to overcome the force of airpressure acting on section 32 and the force of the spring 40, both ofwhich act toward the left as viewed in FIG. 1, moves the element 26, andparticularly the pneumatic section 32, to the right as viewed in FIG. 1.Port 18 communicates with one side of bore 34 and port 20 communicateswith the other, so the presence of section 32 extended into the bore 34completely closes communication between the air inlet port 18 and theair outlet port 20 as shown in FIG. 2 except for leakage, which isnegligible.

Referring to FIG. 1, air can flow freely from air inlet port 18 to airoutlet port 20 in the open position of element 26, transversely throughthe bore 34, to compressed air powered motor M. Motor M drives thehydraulic pump P to pump hydraulic fluid from tank T into line 50 andthrough valve V, when valve V so directs the fluid from line 50 asillustrated in FIG. 1, to actuator A. Line 52 connects line 50 withhydraulic sense port 22 to communicate the pressure of the pump P or theload A to the unbalanced area 30. When the pressure at port 22 reaches ahigh enough value, the force exerted by the hydraulic pressure on area30 urges the valve stem 26 to the right, overcoming the force of spring40, to close bore 34 and stop fluid communication from port 18 to port20. This stops the air motor M which correspondingly stops driving thepump P. However, should the pressure at port 22 go down, spring 40 willovercome the hydraulic fluid force on area 30 to open communicationbetween the air ports 18 and 20 and drive motor M to once again raisethe pressure exerted on the load A until the pressure limit is onceagain reached to turn off the flow of air. Also, should the valve V beactuated so as to retract actuator A by directing the fluid in actuatorA to the tank T (by shifting the valve upwardly to the lower position asillustrated in FIG. 1) and by blocking the flow from pump P, thepressure at port 22 will go up, until it reaches the limit of pressureexerted on area A (area 30) to overcome spring 40 and the air pressureand turn off the air from port 18 to port 20, thereby stopping the pumpP.

A preferred embodiment of the invention has been described inconsiderable detail. Many modifications and variations to the embodimentdescribed will be apparent to those skilled in the art so the inventionshould not be limited to the embodiment described.

We claim:
 1. A hydraulic system, comprising: a source of hydraulicfluid; a hydraulic pump in communication with the source of hydraulicfluid to draw fluid from the source of hydraulic fluid and deliver thefluid under a supply pressure to a supply of hydraulic fluid; a sourceof compressed air; an air motor in communication with the source ofcompressed air that is powered by the source of compressed air to drivethe hydraulic pump; a pressure limiting valve in communication with thesource of compressed air and in communication with the supply pressureof the hydraulic fluid, said valve comprising: a valve housing having anair inlet port in communication with the source of compressed air and anair outlet port and a hydraulic fluid sense port in communication withthe supply pressure of the hydraulic fluid; a valve element in thehousing having a hydraulic section and a pneumatic section, thehydraulic section being in fluid communication with the hydraulic fluidsense port and the pneumatic section being in fluid communication withthe air inlet port and the air outlet port and openable to provide fluidcommunication between the air inlet port and the air outlet port in anopen position and operable to close fluid communication between the airinlet port and the air outlet port in a closed position; wherein thehydraulic section has an unbalanced area in fluid communication with thehydraulic fluid sense port such that a pressure limit at the hydraulicfluid sense port acts on the unbalanced area to move the valve elementto the closed position which moves the pneumatic section into a positionbetween the air inlet port and the air outlet port to block the flow ofair between the air inlet port and the air outlet port.
 2. A hydraulicsystem as claimed in claim 1, wherein the air outlet port is in fluidcommunication with the air motor.
 3. A hydraulic system as claimed inclaim 1, wherein air pressure and a spring urge the valve element to theopen position.
 4. A hydraulic system as claimed in claim 3, wherein theforce of the spring is adjustable.
 5. A hydraulic system as claimed inclaim 1, wherein the hydraulic section and the pneumatic section of thevalve element are integral with one another.
 6. A hydraulic system asclaimed in claim 1, wherein a cartridge portion of the housing defines ahydraulic chamber in which the unbalanced area of the hydraulic sectionresides.
 7. A hydraulic system as claimed in claim 1, wherein the valveelement further comprises a spring section within which a biasing springacts on the valve element.
 8. A hydraulic system as claimed in claim 1wherein the unbalanced area is created by a difference in diameter inthe valve element.